It has been known to measure the physical properties of contact lenses using various devices and methods, i.e. optical metrology. Conventionally, optical metrology involves directing an incident beam at an optical object, measuring the resulting diffracted beam, and analyzing the diffracted beam to determine various characteristics, such as the profile of the structure. However, traditional ophthalmic lenses are often made by cast molding, in which a monomer material is deposited in a cavity defined between optical surfaces of opposing mold parts. To prepare a lens using such mold parts, an uncured hydrogel lens formulation is placed between a plastic disposable front curve mold part and a plastic disposable back curve mold part.
The front curve mold part and the back curve mold part are typically formed via injection molding techniques wherein melted plastic is forced into highly machined steel tooling with at least one surface of optical quality.
The front curve and back curve mold parts are brought together to shape the lens according to desired lens parameters. The lens formulation is subsequently cured, for example by exposure to heat and light, thereby forming a lens. Following cure, the mold parts are separated and the lens is removed from the mold parts for said conventional optical metrology. However, the nature of the injection molding processes and equipment make it difficult to form custom lenses specific to a particular patient's eye or a particular application. Consequently, in prior descriptions, methods and apparatus for forming customized lenses via the use of free-form techniques have been described, such as in WO 2009/025848 and WO 2009/025845. An important aspect of these techniques is that a lens is produced in a novel manner where one of two lens surfaces is formed in a free-form fashion without cast molding, lathing or other tooling on top of a forming mandrel.
As described in corresponding free-form disclosures, such as in WO 2009/025848 and WO 2009/025845, a free formed surface and base may include a free flowing fluent media included in the free formed surface. This combination results in a device sometimes referred to as a lens precursor. Fixing radiation and hydration treatments may typically be utilized to convert a lens precursor into an ophthalmic lens.
A freeform ophthalmic lens created in this manner may need to be measured at different states in order to ascertain the physical parameters of the lens and ensure it meets specified convergence design criteria. Therefore, new apparatus and methods are needed for measuring a thickness profile of said free-formed ophthalmic lenses.